Final answer:
A patient who had a right-sided radical mastectomy and lymphadenectomy should be informed about the signs of lymphedema, which include limb swelling, tight, stretched skin, and pitting edema.
Step-by-step explanation:
The manifestation of lymphedema that a medical assistant should inform a patient who recently underwent a right-sided radical mastectomy and lymphadenectomy about is the swelling of subcutaneous tissues, which could result in increased limb size and tight, stretched skin. Lymphedema occurs due to damage or removal of lymph nodes and vessels, which disrupts normal lymphatic drainage and causes lymph fluid to accumulate. A common test for edema is the pitting test, where persistent indentation after pressing a finger into the swollen area indicates fluid accumulation.